Generally, a deposition apparatus is used to deposit thin films on various electronic parts. In particular, the deposition apparatus is used to form thin films on electronic devices and display devices such as semiconductors, LCDs, organic electroluminescence displays, etc.
Organic electroluminescence displays are electroluminescence displays that inject electrons and holes into emitting layers from electron injecting electrodes (Cathode) and hole injecting electrodes (Anode), respectively. Light is emitted when exitons, coupled with the injected electrons and holes, fall from excited states to ground states.
To improve light-emitting efficiency of the organic electroluminescence display, the holes and electrons are transported to an emitting layer. For this purpose, an electron transfer layer (ETL) may be positioned between the cathode and the organic light-emitting layer, and a hole transport layer may be positioned between the anode and the organic light-emitting layer.
Also, a hole injection layer (HIL) may be positioned between the anode and the hole transport layer, and an electron injection layer (EIL) may be positioned between the cathode and the electron transfer layer.
Generally, thin films are formed on substrates by physical vapor deposition such as vacuum evaporation, ion-plating and sputtering. However, thin films may also be formed by chemical vapor deposition or by gas reactions, etc.
Vacuum evaporation has been used to form thin films, such as metal films, for organic electroluminescence devices and the like.
Indirect heating systems (or induced heating systems) have been used in vacuum evaporation. In such systems, the deposition materials are contained in crucibles and indirect heating systems are used to heat the deposition materials to predetermined temperatures. The apparatuses also include heaters for heating the crucibles, and nozzles for spraying the deposition materials emitted from the heated crucibles onto substrates.
However, these indirect heating systems are expensive since linear metallic heating sources such as Ta, Mo and W are used, and the linear structure yields low heating efficiency.
Also, effective isolation of the heating unit remains a requirement since the heat emitted from the heating unit to heat the crucible is transferred to other regions of the apparatus.
In addition, to achieve the deposition rate required for heating the crucible, electric power is applied to the heating unit at an established reference deposition rate to elevate temperature. The heating unit is sustained at that reference deposition rate until the deposition rate is stabilized. Deposition is performed after stabilization of the deposition rate and during the time in which the deposition rate is stable. However, this deposition method requires excessive amounts of time to stabilize the deposition rate, increasing the amount of time needed for the deposition of materials on the substrate.
Also, the deposition materials evaporate due to irregular heat transfer to the crucible. These evaporated deposition materials condense on the nozzle while flowing toward the substrate, thereby decreasing deposition efficiency and reducing product yield.